For some time, it has been a practice to weld together railway rails to provide improved track over the older bolted-end method of joining rails. Typically, the standard 39 foot rail sections are welded together to form rail strings approximately 1/4 mile in length, the welded rail strings being subsequently transported to the track construction site. The welded rail strings are formed from new rail sections as well as used sections salvaged from old track. Welded rail track was proved so superior to older track construction, that American railroads are systematically replacing bolted rail tracks with newer welded rail.
A number of machines have been developed for welding rail sections, probably the most successful of which is the flash butt welding machine of the type shown, for example, in U.S. Pat. No. 3,488,467. In the flash butt welding process, the rail sections are clamped in precise end to end alignment, and an electrode is attached to each section, the sections are then shifted axially toward and away from one another as current is supplied to the electrodes to preheat the rail ends in a desired manner, and finally the rail sections are upset to effect the weld.
Rail alignment in such flash butt welding machines (and in other welders as well) is of critical importance to the successful welding of rail section. In this latter regard, the rail industry has developed rather rigid tolerances for alignment of rail sections in the interest of safety and improved service life.
While it is desirable that the base and the upright web of adjacent rail sections be properly aligned, it is of prime importance that the heads of the rail sections be precisely aligned since this is the portion of the finished rail which is engaged by the rolling stock. Accordingly, it is preferred to align rail sections by the use of locators which contact the rail head as opposed to other portions of the rail.
New rail sections are relatively easy to align for welding since they generally present a uniform cross section from rail to rail. Thus, when welding a given lot of new rail, the operator may simply make a single alignment set-up and relay upon this to provide accurate alignment for all welds of the lot. However, this is not the case with used rail sections which may vary widely in cross section depending upon the type of track service which they have experienced. Moreover, even used rail sections from the same stretch of track will vary in cross section depending upon the particular location of the section along the track.
Alignment of used rail with non-adjustable locators with contact the rai; head (the preferred method as indicated above) is an especially difficult problem inasmuch as the rail head may be substantially deformed as a result of its contact with the rolling stock. Typical of such deformation is gauge wear which results in a portion of the gauge side of the rail head being eroded adjacent the running surface and head flow which results in an outwardly extending lip being formed on either side of the rail head adjacent the running surface. When either gauge wear or head flow is present, the accuracy of alignment devices having non-adjustable locators which contact the sides of the rail head, may be significantly disturbed.